It is known from the prior art to extensively use casein as the superplasticiser for hydraulically setting formulations, i.e. as an additive which reduces viscosity in order to obtain a suitable flow behaviour. In formulations said casein component leads to particularly good characteristics, which could not hitherto be readily achieved with synthetic superplasticisers.
Casein is a natural product obtainable by acid treatment from milk. However, it suffers from a number of known disadvantages. Thus, casein is available in widely differing qualities and in part at a widely differing price level on the market, so that as a result of the non-constant composition reproducible applications are not possible. In addition, casein-containing formulations are forbidden in certain countries, such as e.g. Scandinavia, because they split off during hydrolysis of the amino groups present, which is not only toxicologically objectionable, but can also lead to the discoloration and damage to other materials.
Therefore there is a need for a material providing a similar performance profile to casein, but without suffering from the above disadvantages. So-called high performance concrete superplasticisers are in part used for this purpose and in the same way as casein-containing systems have good processability, easy handling, but a different performance profile. These superplasticisers are essentially subdivided into four groups, namely sulphonated melamine-formaldehyde condensates, sulphonated naphthalene-formaldehyde condensates, modified lignosuiphonates and a further group from sulphonates, polyacrylates, polystyrene sulphonates, etc. For example, sulphonated melamine-formaldehyde superplasticisers are used to a significant extent, but are losing significance as a result of their tendency to release toxic formaldehyde.
The hitherto known synthetic superplasticisers were mainly developed for concrete, but as a result have in part also been used in mortars. However, the excellent, liquefying action of these known superplasticisers is only maintained for a short time, which is particularly disadvantageous in the case of mechanical processing if a considerable time elapses between production, transportation and use. Moreover, with such synthetic superplasticisers, it is not possible to regulate the honey-like consistency like that provided by casein superplasticisers, so that a completely different performance profile is exhibited.
The prior art has provided proposals attempting to optimize this technology. Thus, JP 08217508 discloses a cement mixture comprising a polyethylene oxide and protein-containing thickener, a superplasticiser, a rapidly hardening agent and a setting retarder.
U.S. Pat. No. 5,494,516 describes a process in which a water-soluble polyalkylene oxide, a β-naphthalene sulphonate-formaldehyde condensate and a superplasticiser, selected from lingosulphate, melamine sulphonate formaldehyde condensate, carboxylates and styrene-maleic anhydride copolymers are brought together. The soluble polyalkylene oxide can be replaced by up to 50% hydroxyalkyl cellulose. It is also possible to use other superplasticisers. Application in conjunction with a spraying on of a cement or mortar composition is very specific.
FR 9 400 170 relates to a casein substitute, composed of a melamine formaldehyde condensate superplasticiser, cellulose, such as hydroxyethyl cellulose and/or a heteropolysaccharide such as xanthan gum.
According to EP 946 617 B1 carboxyl group-containing polymers with polyalkylene oxide ether side chains are used and phosphorus-containing compounds are added during polymerization.
WO 86/00291 describes a cement mixture comprising hydraulically setting cement, one or more flocculants, selected from among sodium alginate, cellulose ether, poly-acrylates, polyacrylamides, guar gum, gelatin, chitosan, dextrin and dialdehyde starches, one or more water-reducing agents selected from among sulphonated naphthalene/formaldehyde condensate, sulphonated melamine/formaldehyde condensate, lignosulphonates, modified lignosulphonates, salts of polyhydroxycarboxylic acids, polyhydroxycarboxylic acids, glucosaccharides, copolymers of linear or cyclic C4- to C6-olefins and unsaturated ethylene dicarboxylic acids, an aggregate and water.
However, the prior art systems fail to provide satisfactory results. When using the above-described, synthetic superplasticisers the water is not retained in a suitable manner in the formulation, e.g. in the mortar, i.e. it is too rapidly lost. This behaviour, i.e. the water retention represents the strength of retention of the water and a suitable water balance must exist. The water losses are caused by an absorbent substrate or evaporation. In order to give such a material a suitable water retention and to prevent separation of the formulation, such materials consequently contain further additives, such as corresponding thickeners. When using excessive quantities of such additives, the viscosity becomes too high and there is a reduction to an unacceptable level of the flow characteristics of the material.